An easy to install method of making “Mechanical Stops”
for the Cab04/06 Engineer Throttles, utilizing the Knob’s two grub screws, to
eliminate heavy fisted operators breaking the Potentiometers.

I mostly use Radio Procabs/Power Cabs on my layout and
I have two radio Cab04s “lying” around, so I thought I’d investigate how hard
it is to fit some “Stops” to my throttles. I haven’t broken any Potentiometers
yet. Testing a Cab06 with an Encoder made me appreciate the positive operation
of the Knob’s “stop”
or Speed Step “0” position of a Potentiometer style of throttle. Hopefully NCE
will release a Cab06PR.

The “Stops” modification took about half an hour and
made a really worthwhile modification that operates perfectly.

Mark a line around the Knob’s circumference at the
10 o’clock position, as shown in the photo.

This position is the only place that allows using
the Knob’s two Grubscrews and some facia material, to hold a “Pin”, without
re-applying the Knob’s Top with the Line.

The Grubscrew shown is provides the “0 Speed” Stop
with the “line” on the Knob at 7.30 o’clock position.

How good is that and I didn’t even have to try hard
– PERFECT.

The Knob rotates 270 degrees, slightly less than what
the “original” Knob rotated with the Potentiometer’s internal 300 degrees
“Stops”.

NCE must have thought about us, when they made this
knob and the facia.

The rotating “Stops” are already in the Knob – the
two Grubscrews. The “OFF” or ZERO Speed Grubscrew painted white in the photo
and the second Grubscrew (90 degrees CCW) is the MAX Speed Stop and is just
visible.

At the corner of the Potentiometer square cut out,
mark an arc 4.6 mm inside the previously pencil marked arc of the knobs
circumference.

Hopefully this will position the hole aligning the
screw right in the middle of the circumferential “Slot” in the Knob.

Drill a 3.0 mm hole through the Cab facia.

Cut/grind away the facia’s
“ribs” to “lower” the screw head for clearance between the Circuit Board and
the screw head.

I used a 3.0 mm screw 12.0 mm long.

Trim the “outside” of the 3.0 mm Nut to provide more
clearance inside the knob. See the above photo and your installation.

I applied some Insulation Tape over the screw head
for some extra protection from contacting the Circuit Board.

I could have used a Self Taper screw but I wanted
the extra strength that a screw and nut provide for those heavy fisted “Old
Farts” that want a Knob throttle on my layout.

Install the Knob making sure the Potentiometer is
fully CCW. If you want, you can turn the Potentiometer a few degrees CW so
the mechanical stop is not “right at” the Potentiometer’s Stop.

Adjustment of Stop: Set 128 Speed Step mode in a test loco. Program CV 2 to provide a fast “take off” at Speed Step 1. This provides visual effect
that the Potentiometer is at Speed Step 1.

With Knob fully CCW against the mechanical stop,
turn Knob slowly CW until the loco jerks forward, that is Speed Step 1.

Make sure there is some “Dead” travel of the
Potentiometer.

The 90 degree spacing for the Knob’s Grubscrews
provides a perfect MINIMUM and MAXIMUM Throttle Stops.

This is why I said NCE was thinking about us.

You can have those Encoder Cab04E throttles but I
need Potentiometers, confirmed by my Aug11 Cab06 test where I hated the
“forever twisting” motion to Stop a loco. NCE, please hurry up with those
Cab06PRs if you are in fact making them.

The Card clipped into the small holder glued to my
Cab04, is an “Operating Card” with all the instructions for a Visitor even
regular operators, to run a train on my layout.